The present invention relates to a semiconductor light emitter, more particularly a light emitter in which a surface of a semiconductor layer serves as a light emission light-transmissive face.
A semiconductor light emitter which has an electric current block function on a surface thereof is proposed, for example, by Japanese Unexamined Patent Publication No. HEI 8(1996)-250769. As shown in FIG. 11, the semiconductor light emitter is so constructed that an N-type layer (semiconductor layer) 200 and a P-type layer (semiconductor layer) 300 are disposed on a sapphire substrate 100 and an electric current block region and an electric current injection region are provided on the P-type layer 300.
In this semiconductor light emitter, the current block region is formed as a current block layer (SiO2) 400 of about 300 nm thickness, and a pad electrode 700 having the same size as the current block layer 400 is formed on the current block layer 400 with intervention of a barrier layer (Ti, Cr or the like) 500 of about 30 nm thickness and a light-transmissive electrode 600.
Further, the current injection region is constructed of a light-transmissive electrode 600 which is formed integrally with a light-transmissive electrode 600 disposed on the current block layer 400, that is, so as to cover the current block layer 400.
The pad electrode 700 is formed of a thick metal film of about 1,000 nm thickness and does not transmit light at all. On the other hand, the light-transmissive electrode 600 is formed of a very thin metal film having a thickness of about 10 nm or less and thus can transmit light to some extent. Therefore, light generated in the semiconductor layer 300 can easily be taken out at a portion where the pad electrode 700 and the current block layer 400 do not exist. Furthermore, since the current block layer 400 is provided below the pad electrode 700 which does not transmit light for blocking the flow of electric current, the light emission efficiency as a whole is improved.
However, since the light-transmissive electrode 600 is much thinner than the thickness of the current block layer 400, disconnection occurs at a sidewall of the current block layer 400 because of a difference in level between the light-transmissive electrode and the current block layer. Accordingly, there arises a problem that the pad electrode 700 and the light-transmissive electrode 600 disposed in the current injection region are not continuously connected and thus the resistance of the light-transmissive electrode 600 rises at this site. For this reason, electric current from the pad electrode 700 cannot be efficiently injected into the P-type layer 300 via the light-transmissive electrode 600 at the sidewall of the current block layer 400. As a result, there arises a problem that the light emitter cannot fulfill its functions of generating light sufficiently and taking out the generated light efficiently.
As a result of the inventors"" earnest study to solve the above-described problems, it has been found that the thickness of the light-transmissive electrode reduces at the sidewall of the current block layer to about one-third to one-tenth of its thickness on a level face and that the disconnection remarkably occurs where the thickness of the light-transmissive electrode becomes one-tenth or less of the thickness of the current block layer. The inventors has also found out that the light-transmissive electrode becomes of high resistance if its thickness decreased to 1 nm or less at the sidewall of the current block layer and that as a result, electric current cannot be efficiently injected to the current injection region. From these findings, the inventor has made various studies on the construction of light emitters which allows an efficiently injection of electric current into the current injection region and also an efficient take-out of the generated light via the light-transmissive electrode, finally to achieve the present invention.
According to the present invention, it thus provides a semiconductor light emitter comprising a semiconductor layer for providing an electric current block region and an electric current injection region on a surface thereof, an electric current block layer formed on the semiconductor layer for defining the electric current block region, a pad electrode formed on the electric current block layer and a light-transmissive electrode formed on the semiconductor layer for defining the electric current injection region, the semiconductor light emitter being characterized in the pad electrode has an electrode connection portion for connection with the light-transmissive electrode.